Moyamoya syndrome (MMS) is a chronic progressive cerebrovascular condition characterized by bilateral stenosis/occlusion of the terminal internal carotid artery (ICA) often extending to neighboring cerebral arteries with prominent collateral circulation and increased risk of hemorrhage. Symptoms include stroke, TIA, and headache.1 MMS’s etiology is unknown. However, experimental evidence from arterial smooth muscle cells (SMC) derived from patients with MMS has suggested that interleukin-1 beta (IL-1β)-dependent prostaglandin overproduction plays a crucial role in its pathogenesis.2 Neonatal onset multisystem inflammatory disease (NOMID) is an autosomal dominantly inherited disease characterized by excessive IL-1β-overproduction and autoinflammation. Accordingly, NOMID is treated with IL-1 receptor antagonists such as anakinra (Kineret, Swedish Orphan Biovitrum AB, Sweden, Stockholm) or IL-1 receptor antibodies such as canakinumab (Ilaris, Novartis, Basel, Switzerland).3 We here report the development of MMS in a NOMID patient. In this patient, escalation of IL-1 receptor antagonistic treatment led to a significant reduction of disease activity and TIAs. Both the occurrence of MMS in this NOMID patient and the clinical and laboratory improvement because of IL-1 receptor antagonism provide direct clinical evidence that IL-1β overproduction could play a pathophysiologic role in MMS.